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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 200px; height: 200px; margin: 100px auto;
            background-color: #ccc;
            box-sizing: border-box;

            border: 10px solid #000;
            padding: 20px;
        }
        /*
            块
                边界, 描边, 填充, 内容
        */
    </style>
</head>
<body>
    <div class="box">
        TestTestTestTestTestTestTestTest
    </div>
</body>
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